The present invention relates to an apparatus and a method which are capable of detecting an internal mechanical failure occurring in a tire in a state where a vehicle having a wheel with the tire mounted thereto is traveling.
In a case where a failure such as a separation (peeling damage between a rubber and a belt constituting a tire or between rubbers) occurs in a tire for some reason during traveling of a vehicle, if the vehicle continues to travel in a state where the failure is occurring, for example, a burst may suddenly occur in the tire to make the traveling impossible, and as a result, there is a possibility that a traffic accident may be caused. In a case where a failure such as a separation occurs in a tire, it is very important in terms of safety to detect the failure rapidly and warn a driver or the like of the failure. For this purpose, a product tire is examined before shipping using, for example, an X-ray nondestructive tester. During production of a tire in a case where there is an internal mechanical failure caused by contamination of a foreign matter or the like in a tire material in molding and vulcanization processes, the internal mechanical failure can be found by the examination before shipping. Further, in a case where it is assumed that the product has low durability from a tire structure, rubber physical properties, and the like, a durability test is previously conducted as a commodity test. In the commodity test, the durability is evaluated by an indoor durability test using drum-type durability test apparatus which is generally conducted, whereby an index of durability as a tire to be actually mounted to the vehicle in the common road is obtained.
However, for example, in the examination before shipping using the X-ray nondestructive tester, although a large separation occurred in the tire can be detected, a separation that is caused by a load during traveling to proceed cannot be detected (predicted). Further, even when the index of durability can be obtained by the indoor durability test using drum-type durability test apparatus, according to the durability test as described above, only a part of a load state (a load capacity, an air pressure, a road temperature, a traveling pattern, etc.) applied to the product tire that is being used in a state where the tire is actually mounted to a vehicle can be reproduced. More specifically, each of the load states of the product tire that is being used in a state where the tire is actually mounted to a vehicle cannot be reproduced individually in the durability test. Presence/absence of the occurrence of the internal mechanical failure such as the separation cannot be predicted exactly for each product tire that is being used in a state where the tire is actually mounted to a vehicle by using only the index of durability obtained by the durability test conducted under limited conditions as described above. Therefore, conventionally, there has been a demand for an apparatus capable of rapidly detecting an internal mechanical failure such as a separation that occurs during traveling of a vehicle for a product tire that is being used in a state where the tire is actually mounted to a vehicle, and a method therefor.
Conventional means for detecting a failure occurring in a tire mounted to a vehicle is disclosed in, for example, JP 2003-80912 A and JP 2003-72330 A. JP 2003-80912 A discloses an abnormality detection system of a tire. JP 2003-90912 A discloses that, according to the tire abnormality detection system, changes in vibration and sound of a tire mounted to a vehicle during traveling are measured, the measurement results are subjected to frequency analysis, and a state of the tire is determined using results of the frequency analysis, whereby a driver can be informed of the abnormality of the tire with accuracy. Further, JP 2003-72330 A discloses a tire monitoring system. JP 2003-72330 A discloses that, according to the tire monitoring system, the air pressure and internal temperature of a tire are detected, and in a case where the air pressure becomes lower than a previously set value and the internal temperature of the tire becomes higher than a previously set temperature, it is determined that there is an abnormality in the tire, whereby a tire blowout and an abnormality state which may cause the tire blowout can be detected.
Patent Document 1 describes that, according to the tire abnormality detection system, the abnormality of a tire is detected based on the measured change in the vibration or sound of a tire. However, in an actual vehicle, the states of the vibration and sound of a tire vary depending on changes of various factors such as a condition of a road surface on which the vehicle actually travels, and traveling conditions (speed and weight) of the vehicle. The variations in the states of the vibration and sound include a number of components corresponding to the changes in the state of the road surface and traveling conditions of a vehicle, i.e., a number of noise components. In the tire abnormality detection system described in JP 2003-80912 A, the abnormality of a tire cannot be detected with sufficient precision due to an influence of the noise components. Further, in the tire monitoring system described in JP 2003-72330 A, an internal mechanical failure of a tire is detected based on the air pressure and internal temperature of the tire. However, the inventors of the present application confirmed that in a state where a failure such as a separation has occurred in the tire, changes do not appear so remarkably in the air pressure and internal temperature of the tire. Specifically, a vehicle with a tire having no internal mechanical failure mounted thereto was allowed to travel continuously for one hour, and the temperature and internal pressure of the tire were detected respectively before and after the traveling. Then, an identical tire (with the same size and air pressure) in which a separation has occurred was mounted to the same vehicle, and the vehicle was similarly allowed to travel continuously for one hour, and the temperature and internal pressure of the tire were detected respectively before and after the traveling. Consequently, irrespective of whether the internal mechanical failure (separation) has occurred in the tire, no change in the internal pressure of the tire was recognized before and after the continuous one-hour traveling, and a significant difference was not recognized in a change of temperature either. With the tire monitoring system described in JP 2003-72330 A, a failure such as a separation occurring in a tire cannot be detected with sufficient precision.